Genetic counseling: Bardet-Biedl Syndrome-2
Bardet-Biedl Syndrome Genetic Etiology *Mode of inheritance: Autosomal Recessive. It requires a recessive mutation in one of six loci plus an additional mutation in a second locus, known as triallelic inheritance. *Chromosome locations: This syndrome is linked to 6 different loci-BBS1 on 11q13, BBS2 on 16q21, BBS3 on 3p13, BBS4 on 15q22.3, BBS5 on 2q31, and BBS6 on 20p12 Incidence and Carrier Frequency *Incidence is 1 in 100,000, with an increased prevalence in Arab and Bedouin populations (1 in 13,500). Carrier frequency is 1 in 179. Clinical Features *Obesity *Eye Problems: Rod-cone dystrophy (major) **Retinitis pigmentosa **Strabismus **Cataracts *Mouth and Tooth Problems: High arched palate **Dental crowding **Hypodontia **Small tooth roots *Cardiac Problems: Left ventricular hypertrophy **Other congenital heart defects **Hypertension *Hepatic Fibrosis *Hirschsprung disease (less than 10% of patients) *Hypogonadism (major) *Undescended testes (10%) *Hypothyroidism *Asthma (27%) *Renal Problems (major): Nephrogenic diabetes insipidus **Irregular kidney contour (fetal lobulation) **Polydipsia and Polyuria (66% of patients) **Recurrent urinary tract infections (30% of patients) *Polydactyly of hands and/or feet (major) *Brachydactyly of hands *Speech delays *Ataxia *Developmental delay *Learning disabilities (major) *Diabetes mellitus (15-45% of patients) *A clinical diagnosis is made with the presence of 4 major features or 3 major and 2 minor features *Age of onset is usually early childhood. *Life span is variable, depending on severity and management of symptoms. Testing *Chromosomal testing is available. This can be done prenatally as well as postnatally. Surveillance, Management, and Treatment Options *In the clinic, fundoscopic examination of the eyes should be performed through dilated pupils as well as blood pressure measurement and urinalysis for glucose, protein and leukocytes. Baseline investigations should include ERG/VER, ECG, echocardiogram, ultrasound of the kidneys and urinary tract and either an IVP or DMSA/DPTA scan. The child should be evaluated by cardiology, opthamology, urology, nephrology, genetics, speech, endocrinology, and orthopedics. It is not possible to cure this condition, but regular follow-up for symptoms can improve quality of life. Psychosocial Issues *Guilt, fear, anger, anxiety, sadness, desperation, and depression are common feelings associated with this diagnosis. It is important to assess the family situation, support system, financial position, and living environment as well as offer any resources to families that may be helpful Support Groups *Retinitis Pigmentosa International :23241 Ventura Boulevard :Woodland Hills CA 91364 :8189920500 :8003444877 :e-mail: rpint@pacbell.net :Home Page: http://www.rpinternational.org *American Foundation for the Blind :11 Penn Plaza :New York NY 10001 :2125027600 :8002325463 :e-mail: afbinfo@afb.org :Home Page: http://www.afb.org *American Printing House for the Blind :1839 Frankfort Avenue :Louisville KY 40206-0085 :5028952405 :8002231839 :e-mail: info@aph.org :Home Page: http://www.aph.org *National Association for Parents of the Visually Impaired :P.O. Box 317 :Watertown MA 02472 :6179727441 :8005626265 :e-mail: napvi@perkins.pvt.k12.ma.us :Home Page: http://www.spedex.com/napvi *Prevent Blindness America :500 East Remington Road :Schaumberg IL 60173 :8478432020 :8003312020 :e-mail: info@preventblindness.org :Home Page: http://www.preventblindness.org *Vision Community Services :23 A Elm St :Watertown MA 02472 :6179264232 :8008523029 :e-mail: mablind@tiac.net :Home Page: http://www.mablind.org *Blind Children's Fund :4740 Okemos Road :Okemos MI 48864-1637 :5173471357 :n/a :e-mail: blindchfnd@aol.com :Home Page: http://www.blindchildrensfund.org *Laurence Moon Bardet Biedl Syndrome :c/o The Foundation Fighting Blindness :Hunt Valley MD 21031 :4107851414 :8883943937 :e-mail: randerson@blindness.org :Home Page: http://www.blindness.org *American Council of the Blind, Inc. :1155 15th Street :Washington DC 20005 :2024675081 :8004248666 :e-mail: info@acb.org :Home Page: http://www.acb.org *National Association for Visually Handicapped :22 West 21st Street :New York NY 10010 :2128893141 :n/a :e-mail: staff@navh.org :Home Page: http://www.navh.org Notes The information in this outline was last updated in 2002. Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling